The use of synthetic dyes began with Perkin's accidental synthesis of mauvein (C.sub.27 H.sub.24 N.sub.4) or "aniline purple" in 1856. Perkin was attempting to synthesize quinine, but recognized the commercial potential of mauvein as a synthetic dye. The synthetic dye industry was the major synthetic organic chemical industry in the early 1900's. Synthetic dyes have now virtually replaced natural or vegetable dyes in the textile industry, relegating natural dyes to use by hobbyists and cottage industries. The annual global sales of synthetic dyes are now estimated to be about $20,000,000,000.
Production and use of synthetic dyes produces serious toxic waste problems. The dye industry has recently attempted to reduce toxic effluents by recharging dye baths, using different dye techniques that are more efficient, recycling and recovering waste, and using computer technology to control the introduction of dyes and chemicals in the bath. Exhaustion rates have been improved in certain facilities to above about 65%; however, the average exhaustion rate remains about 40% and the synthetic dye industry continues to be a major source of pollution, discharging heavy metal salts and other toxic wastes into the environment.
Although the manufacture and use of synthetic dyes remains a major source of pollution, the commercial textile industry has rejected natural or vegetable dyes because such dyes are not reproducible and the dyed fabrics are not lightfast and washfast using present methods. Protein fibers, such as wool, are somewhat easier to dye than cellulosic fibers, and natural dyes are used commercially to a limited extent to dye protein fibers. Indigo remains in use for dyeing denim yarn. Cotton is the primary natural fiber used by the garment industry, accounting for nearly fifty percent of the fibers used. There is, however, no natural dye mordant process for dyeing cotton fibers, fabric or garments which results in a washfast and lightfast garment.
Natural dyes, such as indigo and madder, have been used since the beginning of recorded history; however, it is almost impossible using known techniques to obtain the same dye shade twice in succession with natural dyes, even using the same method. As noted by a major synthetic dye manufacturer, the color-giving molecules in the plants used for dyeing have not been "specifically designed by nature" for transfer to a substrate. Using prior natural dyeing processes, it is often necessary to choose conditions which severely damage the fiber to obtain a suitably dyed fabric. Further, it has not been possible to obtain dyed fabrics which are colorfast after washing and exposure to light, and it has not been possible to obtain a full palette of colors using natural dyes. Thus, the textile industry has generally rejected natural dyes for commercial applications.
The most commonly used mordants for natural dyes are potential sources of toxic waste. Mordants are chemicals that are necessary to chemically fix most natural dyestuffs. The mordant combines with both the dye molecule and the fiber molecule, producing a permanently fixed insoluble "color lake." The insoluble mordant-dye complex that is chemically combined with the fiber in a mordant-dyed fiber is referred to as a color lake. Color lakes are produced with adjective dyes (dyes that require mordant). Color lakes produced by reacting a dye with a metallic salt, such as madder (alizarin) with alum, were also used in inks and paints.
The most commonly used mordants for natural dyes are alum (potassium aluminum sulfate), chrome (potassium dichromate or potassium bichromate), blue vitriol (copper sulfate), ferrous sulfate, stannous chloride, sodium dithionite or sodium hydrosulfite, ammonium hydroxide, cream of tartar (potassium bitartrate), "Glauber's salt" (sodium sulfate), lime, lye (sodium hydroxide), oxalic acid, tannic acid, urea, vinegar (acetic acid) and washing soda (sodium carbonate, also known as soda ash). As will be understood by those skilled in the art, several of these mordants produce toxic waste, but the prior art has failed to produce permanently dyed cellulose fibers or fabric which are lightfast and washfast and which produce a wide range or palette of colors, even using heavy metal salt mordants.
Among the natural dyes long known to man are indigo, madder, cochineal, cutch and osage. The mordants used with natural dyes include chromium, aluminum, iron, copper, tin and other heavy metal and polluting salts. Madder is a vegetable dye produced from species of Rubia, herbaceous perennials grown in Europe and Asia. Preparations of dyes from madder root were used to produce red, yellow and brown colorations prior to the introduction of synthetic dyes. Cochineal is an insect dyestuff indigenous to Mexico which was in use by natives when the Spaniards invaded Mexico in 1518. The insect cochineal is the Coccus cacti which is cultivated in Mexico and Peru for producing carmine red. Stannous chloride was the principal mordant used with cochineal. Cutch or Catechu, also known as Terra japonica, is obtained from various species of mimosa, acacia and areca trees chiefly found in India, Southern Asia and Africa. The commercial dye product is an extract obtained by boiling the wood, trees, leaves and fruit and processing to produce a yellow or olive color, depending upon the mordant used. Osage is a yellow dye from the bark of the Bodark tree. Indigo is a blue dye from the leaves of the indigo plant. Traditionally, no mordants have been used with indigo dyes.
The methods of processing and preparing dye liquors from madder, cochineal, cutch, osage, indigo and other natural dye substances are well-documented in the literature.
There is an urgent need for a natural dye process and mordant composition which can meet the needs of the commercial textile industry, including a full palette of consistently reproducible natural colors which are lightfast and washfast. Further, there is an urgent need for a mordant which does not produce toxic wastes. The mordant composition of this invention meets both of these urgent needs.